In the electronics field, there is a trend toward ever-higher levels of integration or circuit density. This trend has several important benefits. For example, as more circuitry is put into integrated circuits (ICs), an electronic system can use fewer ICs, so that system cost is reduced. Also, as circuitry becomes smaller and more closely spaced, it is capable of running at higher speeds, so that system performance is improved.
However, along with these benefits come complications as well. Higher IC circuit density results in higher heat dissipation in the IC, so that better methods of heat removal must be employed to maintain the device at an acceptable operating temperature. Higher circuit density also results in more interconnections between ICs; and, to maintain high-speed operation, these interconnections must be short. Therefore, IC packages must make numerous reliable interconnections in as little space as possible. And the packages must be as simple and manufacturable as possible to minimize cost.
One particular packaging approach to achieve very high performance has been to removably mount multiple interconnected ICs together in a single package. Generally in such packages the bare ICs are connected by some means to a common substrate having electrical conductors interconnecting the ICs. In this approach, internal interconnections between ICs, such as the datapath in a central processing unit, are confined within the package. Such interconnections are therefore high speed and do not require package pins. These features increase the performance/cost ratio of the system. Also, since the ICs are removably mounted, they may be replaced easily for repair or design revision without risking destruction of the IC or its interconnect.
It is known to employ tape automated bonding, or TAB, to mount one or more ICs on a substrate. For example, a multi-chip package using TAB is shown in U.S. Pat. No. 5,065,280 issued Nov. 12, 1991 to Karnezos et al. In this system, TAB frames are bonded to ICs to connect them to a common flexible circuit substrate. The connection between the TAB frame and the flexible circuit is made either by soldering or by using an additional elastomeric element to compress them together.
Such a TAB system has several drawbacks. Separate manufacturing steps are required to attach the TAB frame to the IC. Also, the connection between the TAB frame and the flexible circuit is problematic: if it is soldered, the IC and TAB frame are not easily removable; if it is a direct connection, the package must have means to compress the TAB frame and flexible circuit together. Finally, the TAB frame can connect only to contact pads on the periphery of the IC, but future ICs will likely have contact pads in their interior area, known as area pads, in addition to peripheral pads. For these reasons and more, an improved multi-chip package is needed.